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exchange 2003 message size limits

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okay, time for me to ask a tech question. i have a problem with limiting the message sizes in exchange 2003.

as you may know, there are four locations in exchange 2003 where one can define a message size limit.

in our exchange organization we have multiple administrative groups (or "sites" in exchange 5.5 terminology). we have only defined global settings, and for various reasons we have no wish to define the other settings. these global settings are set to 10mb. as it turns out if a user sends a mail to someone in the same administrative group, the message limit is indeed 10mb. but if the user sends a mail to someone in a different administrative group, the effective message limit is about 7 or 8mb.

so to allow the 10mb limit for cross administrative group transfers, we have to set the global settings to 13mb. but the side effect is that mails inside the administrative group is now also 13mb. see the problem?

now i know that we can start using the other limiting settings, but again, we don't want that. what i'm hoping to find out is why the global settings are acting so weird when sending mails to a different administrative group. i have already contacted microsoft, and so far, they don't know either.

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This goes way over my head! I've installed exchange, but only ever played with the basic config of it, and that was about 4 years ago.

lol. thanx for the bumps, guys. i admit, posting it was a longshot. it's a problem that i have been investigating for several weeks now. and the microsoft tech that i'm in contact with is just as lost for clues as i am.

it's not a huge problem. our exchange environment isn't broken beyond repair, or something. but it's very inconvenient that we cannot establish a uniform messaging limit, regardless of where the mails are being sent to, to the guy in the next cubicle, or to a colleague in japan. it also might put extra strain on the network when people find out that they can send larger attachments.

When the 8-MB message crossed the routing group boundary through SMTP and arrived at the destination server, it was approximately 33 percent larger than the original message because of the inter-routing group SMTP increase. The message to User2 exceeded 10 MB on the inter-routing group hop when SubmissionContLength was evaluated by the categorizer on the receiving server. The final message had a content size equal to 11,594,558 (11 MB), and the message exceeded the 10-MB Global Limit, thus returning the 5.2.3 delivery status notification.

hi tom, thanx for your reply. yeah, that document is something i already looked at fairly early on, because what it describes is strikingly similar to what we are seeing in our situation. however, tinkering with the options described there, didn't change anything whatsoever.

"Increased overhead of messages with binary attachments traveling between routing groups over SMTP needs to be accounted for when implementing restrictions.

For outgoing SMTP messages being sent between routing groups, Exchange Server will render attachments in the Transport Neutral Encapsulation Format (TNEF), which is base64 or quoted printable rather than binary. This will cause an approximate 33 percent size increase in the messages.

This issue can be solved by increasing the global message restriction size by a factor of approximately one third to accommodate the overhead.

In Exchange Server 2003 native mode, Summary Transport Neutral Encapsulation Format (STNEF) is always used for intra-organization e-mail. Therefore, there is no increase in the message size when going through a routing group connector. In mixed mode, the behavior is unchanged, because STNEF is within routing groups only.

As an example, set a Global Sending Limit of 10 MB and Global Receive Limit of Not Set. Also, do not configure explicit per-user size limits.

Put three users in two routing groups. User1 and User2 are in one routing group, and User3 is in a different routing group connected through SMTP. Send a message from User1 to User2 and User3 containing an 8-MB attachment. You may expect that User2 and User3 would receive the message. However, the actual results are that User2, who is within the same routing group, receives the message as expected, but the message to User3 returns a 5.2.3 delivery status notification.

In this example, User1 did not override the Global Sending Limit with an explicit mailbox Sending Size Limit, so the global limit is enforced.

When the 8-MB message crossed the routing group boundary through SMTP and arrived at the destination server, it was approximately 33 percent larger than the original message because of the inter-routing group SMTP increase. The message to User2 exceeded 10 MB on the inter-routing group hop when SubmissionContLength was evaluated by the categorizer on the receiving server. The final message had a content size equal to 11,594,558 (11 MB), and the message exceeded the 10-MB Global Limit, thus returning the 5.2.3 delivery status notification.

The fix referenced by Microsoft Knowledge Base article 836738, "E-mail messages that are larger than the "Sending message size" delivery option are delivered in Exchange 2000 Server," does not help in this case because the Max Submission value is not reached until the message crosses the inter-routing group boundary." .."

This implies that if you set local settings or connector settings, this will overwrite the global settings that apply the 33% increase on file size due to the overheads of TNEF for inter-organisational routing.

...clunky I know...

btw - do you have a second storage group that you can test this with??

well, the problem with all this is that the document reports this problem to exist in mixed mode. but we are already in native mode, so as per microsoft there should not be a 33% increase, because of the use of stnef.

i have already played with the connector settings and user settings, and subsequent combinations. aside from the fact that we don't want to use these settings, as mentioned before, it turns out that they have no possitive affect on our problem anyway.

what do you mean by using a second storage group for testing? i don't see what difference a seperate storage group would make. besides, we don't have one free anyway. we are already using the maximum 4 storage groups/5 databases on our regional mailbox servers.

"For outgoing SMTP messages being sent between routing groups, Exchange Server will render attachments in the Transport Neutral Encapsulation Format (TNEF), which is base64 or quoted printable rather than binary. This will cause an approximate 33 percent size increase in the messages."

Certainly an interesting problem...hmmm - maybe I am reading this wrong if so my apologies...

I interpret this as meaning that your site is using TNEF, and it being a known issue or shortcoming with a Microsoft bespoke implementation of data transport between routing groups.

As you no doubt are aware, it is entirely possible in a large corporate site for the Exchange environment to be configured up using System Policies for the message storage limits...so different storage limits can be applied to different groups of users using different storage groups.

My understanding is that differing limits between storage groups could also have an impact with sending messages between routing groups...

In Exchange Server 2003 native mode, Summary Transport Neutral Encapsulation Format (STNEF) is always used for intra-organization e-mail. Therefore, there is no increase in the message size when going through a routing group connector. In mixed mode, the behavior is unchanged, because STNEF is within routing groups only.

Click to expand...

mixed mode: stnef for intra routing group mails only, tnef for inter routing group mails so 33% increase is likely.
native mode: stnef for both intra and inter routing group mails, no increase should appear.

[edit1] [edit2] deleted edit1. my bad. please ignore

as for the storage groups, i see now where you want to go with that. however, that only applies to storage limits (limiting the size of a mailbox), not to individual mail sizes (limiting the size of a sent/received email).

Does the site consist of several child domains?? - as I wonder if the Schema is consistent with Exchange 2003 extensions across all child domains?

For this scenario to occur one of the child domains *might have* had a Exchange 2003 server on a Windows 2000 server, at some stage prior to being upgraded to Windows 2003 with Exchange 2003 in full native mode....this could possibly be an issue.

Does the site consist of several child domains?? - as I wonder if the Schema is consistent with Exchange 2003 extensions across all child domains?

Click to expand...

please define site. exchange 2003 doesn't know sites anymore. you mean administrative group/routing group? or an active directory site?
basically the situation is this. we have one forest, with an empty root domain and five child domains (europe, asia, india, america and head quarters). We have one administrative group/routing group (no distinction in our environment) per child domain, meaning that each region has its own mailbox server (hosting approx 3000 mailboxes each, except hq, which is at 200 mailboxes) and its own bridgehead servers. routing group connectors exist between each routing group.

For this scenario to occur one of the child domains *might have* had a Exchange 2003 server on a Windows 2000 server, at some stage prior to being upgraded to Windows 2003 with Exchange 2003 in full native mode....this could possibly be an issue.

i know for a fact that this didn't happen. together with a handful of colleagues, we are at the top of the admin foodchain for the whole enterprise. we are the only ones with enough access rights, and being the true admin dictators we are, we are in tight control of server deployment. also, we meticulously planned and implemented our new exchange environment. even if a rogue exchange server ever was installed, we would have noticed.

Also you dropped and recreated the routing group connectors?
[might be interesting in a big production environment.. ]

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